Calculus is composed of both inorganic (mineral) and organic (cellular and extracellular matrix) components. The mineral proportion of calculus ranges from approximately 40-60%, depending its location in the dentition. Calculus consists primarily of calcium phosphate crystals organized into four principal mineral phases: octacalcium phosphate, hydroxyapatite, whitlockite, and brushite. The organic component of calculus is approximately 85% cellular and 15% extracellular matrix. Cell density within dental plaque and calculus is very high, consisting of an estimated 200,000,000 cells per milligram. The cells within calculus are primarily bacterial, but also include at least one species of archaea (Methanobrevibacter oralis) and several species of yeast (e.g., Candida albicans). The organic extracellular matrix in calculus consists primarily of proteins and lipids (fatty acids, triglycerides, glycolipids, and phospholipids) as well as extracellular DNA. Trace amounts of host, dietary, and environmental micro-debris are also found within calculus, including salivary proteins, plant DNA, milk proteins, starch granules, textile fiber, and smoke particles.
Sub-gingival calculus (tartar) is composed almost wholly of two components: fossilized anaerobic bacteria whose biologic composition has been replaced by calcium phosphate salts, and calcium phosphate salts that have joined the fossilized bacteria in calculus formations. The initial attachment mechanism and the development of mature calculus formations are based on an electrical charge. Unlike calcium phosphate, the primary component of teeth, calcium phosphate salts exist as electrically unstable ions. The following minerals are detectable in calculus by X-ray diffraction: brushite (CaHPO4.2H2O), Octa calcium phosphate (Ca8H2(PO4)6.5H2O), magnesium-containing whitlockite (Ca9(MgFe)(PO4)6PO3OH), and carbonate-containing hydroxyapatite (approximately Ca5(PO4)3(OH) but containing some carbonate).
The reason fossilized bacteria are initially attracted to one part of the sub-gingival tooth surface over another is not fully understood; once the first layer is attached, ionized calculus components are naturally attracted to the same places due to electrical charge. The fossilized bacteria pile on top of one another, in a rather haphazard manner. All the while, free-floating ionic components fill in the gaps left by the fossilized bacteria. The resultant hardened structure can be compared to concrete; with the fossilized bacteria playing the role of aggregate, and the smaller calcium phosphate salts being the cement. The once purely electrical association of fossilized bacteria then becomes mechanical, with the introduction of free-floating calcium phosphate salts. The “hardened” calculus formations are at the heart of periodontal disease and treatment.
As a summary, in general dental calculus (Sub-gingival) consists of inorganic (70% to 90%) and organic components. The inorganic portion consists mainly (70-80%) of calcium phosphate, Ca3(PO4)2; calcium carbonate (3-5%), CaCO3; and traces of magnesium phosphate, Mg3(PO4)2, and other metals. The percentage of inorganic constituents in calculus is similar to that in other calcified tissues of the body.
The principal inorganic components are calcium, about 40%; phosphorus, about 20%; carbon dioxide, about 2%; magnesium, about 1%; and trace amounts of sodium, zinc, strontium, bromine, copper, manganese, tungsten, gold, aluminum, silicon, iron, and fluorine.
At least two thirds of the inorganic component are crystalline in structure. The four main crystal forms and their percentages are as follows:
Hydroxyapatite, approximately 58%
Magnesium whitlockite, approximately 21%
Octacalcium phosphate, approximately 12%
Brushite, approximately 9%
The organic content of dental calculus (Sub-gingival) consist of a mixture of: protein-polysaccharide complexes, epithelial cells, leukocytes, and various types of microorganisms. 2-10% of the organic component are carbohydrate, which consists of galactose, glucose, glucuronic acid, galactosamine, and sometimes, galacturonic acid, and Glucosamine.
There are few effective ways to prevent the buildup of calculus: through daily tooth brushing and flossing (which removes dental plaque) and regular cleaning visits based on a schedule recommended by the dental health care provider. Calculus accumulates more easily in some individuals, requiring more frequent brushing and dental visits. Smoking and diabetes are external factors that facilitate the accumulation of calculus. Toothpaste with an additive ingredient of zinc citrate has been shown to produce reduction in plaque accumulation.